Remediation of Metal-Contaminated Soil by an Integrated Soil Washing-Electrolysis Process

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<ul><li><p>This article was downloaded by: [Eindhoven Technical University]On: 17 November 2014, At: 08:52Publisher: Taylor &amp; FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registeredoffice: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK</p><p>Soil and Sediment Contamination: AnInternational JournalPublication details, including instructions for authors andsubscription information:</p><p>Remediation of Metal-ContaminatedSoil by an Integrated Soil Washing-Electrolysis ProcessShih-Hsien Chang a , Kai-Sung Wang a , Chung-Yih Kuo a , Chih-YuanChang a &amp; Ching-Tung Chou aa Department of Public Health , Chung-Shan Medical University ,Taichung, Taiwan, ROCPublished online: 18 Jan 2007.</p><p>To cite this article: Shih-Hsien Chang , Kai-Sung Wang , Chung-Yih Kuo , Chih-Yuan Chang &amp; Ching-Tung Chou (2005) Remediation of Metal-Contaminated Soil by an Integrated Soil Washing-ElectrolysisProcess, Soil and Sediment Contamination: An International Journal, 14:6, 559-569</p><p>To link to this article:</p><p>PLEASE SCROLL DOWN FOR ARTICLE</p><p>Taylor &amp; Francis makes every effort to ensure the accuracy of all the information (theContent) contained in the publications on our platform. However, Taylor &amp; Francis,our agents, and our licensors make no representations or warranties whatsoever as tothe accuracy, completeness, or suitability for any purpose of the Content. Any opinionsand views expressed in this publication are the opinions and views of the authors,and are not the views of or endorsed by Taylor &amp; Francis. The accuracy of the Contentshould not be relied upon and should be independently verified with primary sourcesof information. Taylor and Francis shall not be liable for any losses, actions, claims,proceedings, demands, costs, expenses, damages, and other liabilities whatsoever orhowsoever caused arising directly or indirectly in connection with, in relation to or arisingout of the use of the Content.</p><p>This article may be used for research, teaching, and private study purposes. Anysubstantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,systematic supply, or distribution in any form to anyone is expressly forbidden. Terms &amp;Conditions of access and use can be found at</p><p></p></li><li><p>Soil &amp; Sediment Contamination, 14:559569, 2005Copyright Taylor &amp; Francis Inc.ISSN: 1532-0383 print / 1549-7887 onlineDOI: 10.1080/15320380500263758</p><p>Remediation of Metal-Contaminated Soil by anIntegrated Soil Washing-Electrolysis Process</p><p>SHIH-HSIEN CHANG, KAI-SUNG WANG, CHUNG-YIH KUO,CHIH-YUAN CHANG, CHING-TUNG CHOU</p><p>Department of Public Health, Chung-Shan Medical University, Taichung,Taiwan, ROC</p><p>Chelating agents such as EDTA and DTPA are often used to remove metals from soil.However, their toxicity, bio-recalcitrance, and problems with recovery of heavy metaland chelating agents severely limit their applications. A biodegradable chelating agent,LED3A, and two surfactants, SDS and Triton X 100, were evaluated as potential alter-natives for remediation of metal-contaminated soil.</p><p>LED3A alone only removed 40% of cadmium the addition of surfactant signif-icantly enhanced its cadmium removal capacity up to 80% for a wide range of pH(5 to 11). The enhancement increased with both surfactant concentrations and LED3Aconcentrations. Because LED3A had a much higher removal capacity for copper, thesynergistic effect of surfactant-LED3A mixture was less obvious. Sequential extractionanalysis indicated that the LED3A not only removed copper from carbonate and Fe-Mnoxide fraction, but also from organic fractions. A three-dimension electrolysis reactorcould effectively recover both metals and LED3A-SDS within thirty minutes. The com-bined soil washing by LED3A-surfactants and electrolysis provides a potential approachfor remediation of copper- and cadmium-contaminated soils.</p><p>Keywords Soil washing, sequential extraction, LED3A, electrolysis.</p><p>1. Introduction</p><p>The presence of heavy metals in soil poses risks to health and the environment. Soil wash-ing is an inexpensive and practical technique for metal removal. The use of diluted acidscan dissolve soil matrix and damage soil physiochemical and biological properties (Baronaet al., 2001). Chelating agents such as ethylene diamine tetraacetic acid (EDTA) and di-ethylene trinitrilo pentaacetic acid (DTPA) have proven effective in removing metals fromsoils (Peters, 1999; Hong et al., 2002). Their biotoxicity, biorecalcitrance, and problemswith recovery of heavy metals and extracting agents from supernatant severely limit theirapplications (Hong et al., 2002).</p><p>Surfactants are amphiphilic molecules with a hydrophilic head group and a hydropho-bic tail group. Based on their hydrophilic head groups, surfactants can be divided into threecategories: anionic, cationic, and nonionic (Huang et al., 1997). Surfactants at low con-centrations exist as monomers and adsorb onto surfaces and interfaces. When surfactant</p><p>This study was supported by the National Science Council of Taiwan under contract NSC91-2211-E-040-001.</p><p>Address correspondence to S.-H. Chang, Department of Public Health, Chung-Shan MedicalUniversity, Taichung 402, Taiwan, ROC. E-mail:</p><p>559</p><p>Dow</p><p>nloa</p><p>ded </p><p>by [</p><p>Ein</p><p>dhov</p><p>en T</p><p>echn</p><p>ical</p><p> Uni</p><p>vers</p><p>ity] </p><p>at 0</p><p>8:52</p><p> 17 </p><p>Nov</p><p>embe</p><p>r 20</p><p>14 </p></li><li><p>560 S.-H. Chang et al.</p><p>concentrations increase above a certain level (i.e. critical micelle concentration, CMC), themonomers aggregate to form micelles, which have a hydrophobic interior and a hydrophilicexterior (Haigh, 1996). Although anionic surfactants could increase heavy metal removalfrom soil, they are much less effective compared to chelating agents (Nivas et al., 1996;Doong et al., 1998; Gadelle et al., 2001). The information on interactions of chelatingagents and surfactants on soil metal removal is scarce.</p><p>Sequential extraction analysis can help identify the geochemical fractions of metalsin soil (Tessier et al., 1979). Basically, the more stable the metal binding is with the soil,the stronger extractants are required. Heavy metals in exchangeable and carbonate formsare easily solubilized by acids. In contrast, heavy metals bound to organic and crystallinelattice are difficult to extract (Gleyzes et al., 2002).</p><p>LED3A (Lauroyl-ED3ANa2, Dow company) is structurally similar to EDTA. It hypoth-esizes that LED3A should have a similar metal extractive capacity as that of EDTA. Thepresence of anionic surfactant (SDS) and nonionic surfactants (Triton X-100) may affect themetal extractive capacity of LED3A because it poses hydrophobic portion (lauryl functiongroup). In this study, the effects of extractants (surfactants, chelating agent, and surfactant-chelating agent mixture) on cadmium and copper removal at different soil solution pH wereinvestigated. Second, sequential extraction analysis was conducted to determine extractivecapacities of extractants to remove metal from different geochemical fractions. Finally,electrolysis was performed to recover metal from soil-washing solution. The objective ofthis study is to assess the feasibility of the integrated soil washing-electrolysis process formetal-contaminated soil remediation.</p><p>2. Materials and Methods</p><p>2.1 Soil Preparation</p><p>The soil was taken from a park on the Chung-Shan Medical University campus. It wassieved (90% purity, Sigma, USA), Na2EDTA2H2O (100% purity,Tedia, USA), and LED3ANa2 (30%, Hampshire Chemical Corp., USA) (Table 1). Toprepare the different extractants, first, two-fold desired concentrations of surfactant (orchelating agent) were prepared with distilled water. To prepare the desired surfactant-alone(or chelating alone) solution, the 20 ml of surfactant solution was mixed with 20 ml ofdistilled water. To obtain desired surfactant-chelating agent solution, 20 ml of 4, 0.4, 0.04,0.004, 0% of surfactants (SDS or Triton X-100) and 20 ml of 0.02, 0.01, 0.002, 0.001, and0 M of LED3A were mixed. The extractant solution was adjusted to desired pH by NaOH</p><p>Dow</p><p>nloa</p><p>ded </p><p>by [</p><p>Ein</p><p>dhov</p><p>en T</p><p>echn</p><p>ical</p><p> Uni</p><p>vers</p><p>ity] </p><p>at 0</p><p>8:52</p><p> 17 </p><p>Nov</p><p>embe</p><p>r 20</p><p>14 </p></li><li><p>Remediation of Metal-Contaminated Soil by Washing-Electrolysis Process 561</p><p>Table 1Properties of surfactants and chelating agent used in this study</p><p>Type Chemical formula MWCMC mM(mg L1)</p><p>Triton X 100 Nonionic surfactant C12H25O(CH2CH2O)4H 647 0.18 (268)1</p><p>SDS Anionic surfactant C12H25OSO2ONa 288 8.4 (2420)2</p><p>EDTA-Na2 Chelating agent C10H12N2Na2O82H2O 372.2 NA3LED3A-Na2 Anionic surfactant/ Lauroyl-ED3ANa2 459 4 (1700)4</p><p>chelating agent</p><p>1Edwards et al., 1994.2Deshpande et al., 1999.3Chelating agent, NA = not applicable.4Crudden et al., 1994.</p><p>or HNO3 solution. 40 ml of extractant was added into 5 g of metal-contaminated soil in apolyethylene centrifuge tube and mixed on a reciprocating shaker at 30 rpm for 3 hours.</p><p>The soil-washing supernatant was removed by centrifugation (1500 rpm, 30 min),filtered by a Whatman 42 filter paper (2.5m, Whatman, USA), and then analyzed byatomic absorbance spectrophotometry (AAS, Perkin-Elmer, model 3300). Distilled waterwas used to extract the residual extracting solution by following the same procedure, exceptthat the extracting period was shortened to one hour. All experiments were performed intriplicate. Blank control was performed throughout the experiment. For quality control, theartificially contaminated soils were digested in aqua regia and analyzed by AA. Recoveriesof cadmium and copper were in the range 85115%.</p><p>2.3 Sequential Extraction Procedure</p><p>The sequential extraction analysis was conducted as described by Tessier et al. (1979),except that the aqua regia digest method was used in the final extraction rather than digestionwith HF-HClO4 mixture. This was because the soil was artificially spiked, and because itis believed that metals in mineral crystal structure are difficult to redistribute and are notlikely to be mobilized.</p><p>2.4 Electrolysis Test</p><p>All electrolysis tests were conducted with a potentiostat-galvanostat (GW, GPC-3030D,Taiwan). A 400 ml soil-washing solution containing metal (either 4 mg L1cadmium or50 mg L1copper), 0.01M LEAD3A and 2% SDS was used for electrolysis tests. Stainlesssteel wool (0.5 mm width, total area: 600 cm2) and stainless plate (3 cm 8 cm) were usedas anode and cathode, respectively. The current density was maintained at 50A m2. Theanode was wrapped with nylon net to separate the two electrodes.</p><p>3. Results and Discussion</p><p>3.1 Effects of Soil Solution pH on Metal Extraction</p><p>Concentrations of 2% (w/w) surfactants (SDS: 69 mM; Triton X 100: 31 mM) and0.01 M LED3A were used to evaluate their effects on cadmium (20 mg kg1) and copper</p><p>Dow</p><p>nloa</p><p>ded </p><p>by [</p><p>Ein</p><p>dhov</p><p>en T</p><p>echn</p><p>ical</p><p> Uni</p><p>vers</p><p>ity] </p><p>at 0</p><p>8:52</p><p> 17 </p><p>Nov</p><p>embe</p><p>r 20</p><p>14 </p></li><li><p>562 S.-H. Chang et al.</p><p>(400 mg kg1) removal. The applied concentrations of 2% surfactants were based on theconcentrations commonly used in soil washing for removal of hydrophobic organic hy-drocarbons (Mulligan et al., 2001). 0.01 M of chelating agent was determined to be theoptimum dosage for maximal metal removal efficiency (data not shown).</p><p>The use of water, SDS, or Triton X 100 only had little effect (</p></li><li><p>Remediation of Metal-Contaminated Soil by Washing-Electrolysis Process 563</p><p>extract metal from soil, while surfactants do not have any chelating properties. LED3Aremoved cadmium between 3050% depending on soil solution pH and removal in-creased with higher pH. Although LED3A is structurally similar to EDTA, LED3A hada lower cadmium removal capacity than that of EDTA. It is possible that the hydropho-bic portion of LED3A may sorb onto soil and reduce its cadmium removal capacity.However, the addition of either anionic surfactant (SDS) or nonionic surfactant (TritonX 100) significantly increased the cadmium removal by LED3A (&gt;80%), except forLED3A-SDS when soil solution pH was </p></li><li><p>564 S.-H. Chang et al.</p><p>Figure 2. The effects of LED3A-SDS and LED3A-Triton X 100 mixtures on cadmium removal.The spiked cadmium concentration in soil was 20 mg kg1. Each point represents the mean andstandard deviation. The pH of soil solution was 7. (a) The mixture of LED3A-SDS; (b) the mixtureof LED3A-Triton X 100.</p><p>did not inhibit cadmium removal by LED3A. It is possible that Triton X100 is not likely tointeract with cadmium ions.</p><p>Because of the higher copper removal efficiencies of LED3A, only 0.5%, 0.1%, and 2%of surfactants were used to investigate the interactions of surfactants and LED3A on copperremoval (Figure 3). The spiked copper concentration (400 mg kg1) was much higher thancadmium (20 mg kg1). Even though LED3A alone had high copper removal efficiencythe synergistic effects by additions of surfactants were still observed. This suggests that</p><p>Dow</p><p>nloa</p><p>ded </p><p>by [</p><p>Ein</p><p>dhov</p><p>en T</p><p>echn</p><p>ical</p><p> Uni</p><p>vers</p><p>ity] </p><p>at 0</p><p>8:52</p><p> 17 </p><p>Nov</p><p>embe</p><p>r 20</p><p>14 </p></li><li><p>Remediation of Metal-Contaminated Soil by Washing-Electrolysis Process 565</p><p>Figure 3. The effects of LED3A-SDS and LED3A-Triton X 100 mixtures on copper removal. Thespiked copper concentration in soil was 400 mg kg1. Each point represents the mean and standarddeviation. The pH of soil solution was 7. (a) The mixture of LED3A-SDS; (b) the mixture of LED3A-Triton 100.</p><p>Triton X 100 micelles partition copper-LED3A complex, and thus enhance copper removalby LED3A.</p><p>3.3 Sequential Extraction Analysis</p><p>After soil washing by different extractants (water, surfactants, LED3A, or surfactant-LED3A mixture), sequential extraction analysis was performed to determine metal</p><p>Dow</p><p>nloa</p><p>ded </p><p>by [</p><p>Ein</p><p>dhov</p><p>en T</p><p>echn</p><p>ical</p><p> Uni</p><p>vers</p><p>ity] </p><p>at 0</p><p>8:52</p><p> 17 </p><p>Nov</p><p>embe</p><p>r 20</p><p>14 </p></li><li><p>566 S.-H. Chang et al.</p><p>Figure 4. Results of sequential extraction analysis for cadmium and copper in spiked soil after soilwashing by 2% SDS, 0.01M LED3A, and SDS-LED3A mixture. (a) 20 mg kg1 cadmium; (b) 400 mgkg1 copper.</p><p>speciation in soil. The results of sequential extraction analysis provided valuable infor-mation on the metal extractive capacity of different extractants. Water removed less than2% cadmium and copper (Figure 4). Although both cadmium and copper were introducedin the soil by spiking with metal inorganic salts, the speciation distribution of copper wassignificantly different from that of cadmium. In the water-washed soil, most of the cad-mium was in the exchange fraction (70%), followed by carbonate (25%), and Fe-Mn oxidefraction (3%). In contrast, most of the copper was in the carbonate fraction (75%), followedby Fe-Mn oxide (22%), and organic fraction (2%).</p><p>Dow</p><p>nloa</p><p>ded </p><p>by [</p><p>Ein</p><p>dhov</p><p>en T</p><p>echn</p><p>ical</p><p> Uni</p><p>vers</p><p>ity] </p><p>at 0</p><p>8:52</p><p> 17 </p><p>Nov</p><p>embe</p><p>r 20</p><p>14 </p></li><li><p>Remediation of Metal-Contaminated Soil by Washing-Electrolysis Process 567</p><p>Figure 4 shows that 2% of SDS only removed a small amount of cadmium and copper.The addition of 0.01M LED3A alone significantly removed cadmium and copper from soilin all diff...</p></li></ul>


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